Paper No. 6
Presentation Time: 9:40 AM
SURFICIAL QUARTZ SAND DEPOSITS ON THE ATLANTIC COASTAL PLAIN: EOLIAN, FLUVIAL OR MARINE? THE CASE FOR A CATASTROPHIC DELIVERY MECHANISM
Regions of the Atlantic Coastal Plain are often capped by a surficial sheet of quartz sand. For example, the Pinehurst Formation sands are mapped as a separate unit, distinct from the well-provenanced terraces below. The Goldsboro Ridge sand is also distinct, resting on the Sunderland formation. From the Carolina Sandhills eastward to the coast at Wilmington, a nearly continuous and occasionally thick (up to 10m) sheet of high purity quartz sand is blanketed across the intervening terraces and scarps. While the Coastal Plain surfaces show evidence of eolian reworking, studies of the deeper extents of these sandy deposits often mention difficulties in determining their geomorphology, although deemed as gradualistic eolian, fluvial or marine. Marine deposition is appropriate at the coastline, supported by glacial-driven sea level transgressions; but they contain no shell fragments. Inland, deposition on interfluvials during flooding of is reasonable; but these are coarsely skewed, showing no sorting or channeling and minimal clays. At higher elevations, workers implicate eolian deposition on undissected terrain; but delivering coarse sand upslope from distant drainage mandates powerful winds. Oriented ovoid Carolina bay depressions have evolved in these sand sheets, seemingly without deforming or altering the antecedent strata and paleosols they rest upon. They are present in prodigious quantities and may represent diagnostic markers for these distinct sand deposits. In an attempt to identify a universal mechanism for the materialization of these sand sheets, we speculate on an aerial deposition, mobilized and delivered as a "rain" of pulverized distal ejecta emanating from a cosmic impact. The bay depressions may be artifacts of steam outgassing, frozen in time as the sand transited from liquefaction to lock-up, preserving an arrival vector in their orientation. Using data from our LiDAR-augmented geospatial survey of 30,000 Carolina bays, we note systematically varying orientations and robust adherence to archetype planforms. A triangulation network, built using bay orientations and considering the Coriolis steering of trajectories, suggests a probable source impact site. While such a catastrophic mechanism is unorthodox, our survey data and analysis suggests further research is warranted.